Hi! I believe I can be of help with this issue.
First, let me say I can imagine how confusing and distressing this situation must have been for your friend. That she still remembers it and it still has a haunting effect on her is a testament to the power of our minds and emotions.
And this is actually the key to my answer to you that you need to consider and think about. What she experienced is what is called a dissociative episode or state. She had one isolated experience and that is good. It did not indicate anything harmful.
In psychological practice, if someone is experiencing dissociation, meaning that they are withdrawing from the reality of the present and feeling themselves going further and further inside or away or becoming smaller and smaller or into a dream state, then we know that very severe trauma occurred in the person's life and we have to treat it.
The most extreme case of this is called Dissociative Identity Disorder. This is when the person not only feels themselves becoming smaller and more remote from the present reality, but they "disappear" and another personality takes over. This occurs when there was horrific trauma in the person's past.
But if as a child she experienced only one dissociative state and it was brief and mild as this, then it may have been just a childhood experience with no cause for her to find. It may have resulted from some stress that occurred that maybe frightened her. Or it could have been just an entering into a dream state.
Psychology now is exploring these altered consciousness states, notably the meditative states that yogis can achieve. And the results are very fascinating in the psychology of consciousness. Your friend was clearly not trained in these "higher" states of consciousness, but we know that the brain can enter those states and she may have entered such a state accidentally.
So, the way we measure it is by its effect and her state had a benign effect, which is good.
I wish you the very best!
Please remember to click the green accept button. Feel free to continue the discussion; my goal is to get you the best answers possible. Bonuses are always appreciated! If I can be of further help with any issue, just put "for Dr. Mark" in the front of your new question, and I'll be the one to answer it. All the best, Dr. Mark